Hollow chamber profile made of metal, especially for heat exchangers

ABSTRACT

The invention relates to a hollow chamber profile made of metal, especially for heat exchangers. Said profile is made of an extruded base profile ( 10 ) having two broad parallel sides and two narrow sides or is made of a base profile which is a circular tube type or coaxial tube type. At least one channel ( 11 ) extends inside said base profile in the longitudinal direction thereof. The hollow profile has improved heat transfer properties on the sides and webs ( 13 ) which are deformed perpendicular to the longitudinal direction thereof.

The invention pertains to a hollow-chamber profile made of metalespecially for heat exchangers, consisting of an extruded base profile,which has the form of a hollow tube or coaxial tube or has two parallelwide sides and two narrow sides, where at least one channel extendslongitudinally through the interior of the base profile.

This design of a hollow-chamber profile for heat exchangers is knownfrom German Registered Design DE 94 06 559 U1. Here, a simple method bywhich the webs which form the channels are shaped during the extrusionprocess is described. The webs are profiled not after extrusion butduring the extrusion process itself. For this purpose, the webs whichare to be profiled with corrugations are supplied with more extrusionmaterial than the webs which are not to be corrugated. This increasedsupply of material to be extruded leads to the upsetting of the materialand thus to an intentional deformation of the extruded web. Thistherefore represents a simple method for increasing the surface area ofthe web, which leads to improved heat transfer. The intentionaldeformation of the webs, however, leads to the fact that the channellocated between two of these deformed webs has a series of constrictedand expanded sections distributed along the length of the profile. Avariation of this type in the flow cross section leads to pressurelosses and thus to a decrease in the heat-exchange output.

A cooler tube, furthermore, is known from DE 100 49 987 A1. This tubehas ring-shaped corrugations at regular intervals, which projectradially outward and are produced by the axial upsetting of thepreviously smooth cylindrical tube. Smooth cylindrical sections remainbetween the corrugations. A tube of this type, because of its increasedoutside surface area, has better heat transfer properties than a smoothtube. But because the free flow cross section is increased at the pointsof the tube where a ring-shaped corrugation is present, pressure lossesoccur in the medium flowing through the tube, and there is thus a lossof heat exchange performance in this case also. This tube also suffersfrom the disadvantage that the strength of the tube is affected by theaxial compression performed as a follow-up operation.

Profiles of sheet aluminum shaped by rolls are used as an alternative toextruded aluminum tubes or multi-chamber hollow profiles. These profilesare often closed by high-frequency welding or by suitable shaping,followed by brazing. The heat-exchange properties can be improved by theuse of turbulators. The disadvantage of this method is the high cost ofproducing and installing the turbulators. In addition, the brazed orwelded tube seams are frequently a cause of failure under mechanical orcorrosive stresses. The task can be accomplished only partially by theuse of extruded aluminum profiles. Although the seams are much stronger,the suitability for heat exchange is limited by the tube walls and tubewebs, which are shaped only in the extrusion direction. Optimal heattransfer cannot be achieved, especially in the case of gaseous mediasuch as the air in charge coolers or the CO₂ or refrigerant gases usedin air-conditioning heat exchangers.

The task of the invention is to make available hollow-chamber profiles,especially for heat exchangers, which have better heat-exchangeproperties than conventional extruded profiles and which can also beproduced easily.

This task is accomplished according to the invention by a hollow-chamberprofile of metal with the features cited in claim 1 or claim 5 and by aprocess according to claim 8.

The inventive hollow-chamber profile of metal, especially for a heatexchanger, is made from a base profile, which consists preferably of acorrosion-resistant, brazeable aluminum alloy such as a 1xxx, 3xxx, or6xxx alloy. The extruded base profile has the form of a round tube orcoaxial tube or the form of a flat tube with two parallel wide sides andtwo narrow sides, which connect the wide sides together. The interiorspace of the base profile is formed by at least one channel extending inthe longitudinal direction. Opposite sides of the base profile areshaped in a direction perpendicular to its longitudinal orientation,where left-oriented profilings alternate with right-oriented profilings.These profilings are coordinated with each other in such a way that thewidth of the base profile remains the same over its entire length.

In the case of a profile in the form of a flat tube, this shaping,according to the invention, applies both to the narrow sides and to thewebs which extend from wide side to wide side of the base profile toform several channels. In each case, the narrow sides and the webs areprofiled in exactly the same way. This is achieved in that all theshaping operations are performed simultaneously and identically. If, forexample, corrugations are to be provided down the length of the baseprofile, the left-oriented and right-oriented profilings will alternatewith each other in the direction transverse to the longitudinaldirection, so that the crests of the waves of the corrugations of thewebs and of the two narrow sides engage in the corresponding valleys ofthe corrugations of the adjacent webs or narrow sides.

In the case of a tubular profile, especially a coaxial tube with severalchannels in the longitudinal direction, such shaping is provided both onthe outside surface and on the webs which form the channels. In eachcase, here, too, the outside surface and the webs are profiled inexactly the same way.

It is preferable for the amplitudes of the corrugations of the shapedsides and of the webs to be of uniform height along the entirehollow-chamber profile; this also applies to the wavelengths of theprofiling. To obtain high convection rates with good heat transfer atall points, however, it is not absolutely necessary for the corrugationsto have the same wavelengths and the same amplitudes throughout. But ifthe wavelength or the amplitude of one such set of corrugations changes,this must also apply in the same way to the corrugations of the adjacentwebs and also to the sides, so that there will never be a point at whichtwo adjacent walls come closer to each other than they do at any otherpoint. The shaping will therefore never change the flow cross section ofthe channels. The shaping does, however, create turbulence in the gas orliquid stream flowing through the profile. This turbulence is comparableto that produced by the known turbulators, which can also be used insuch devices. A corrugated profile of this type can be used to increasethe heat-exchange output of a gas or liquid stream, although the effectis usually less pronounced with liquids. A hollow-chamber profile ofthis type can be used advantageously as a cooler, especially as a CO₂gas cooler, or as an aftercooler for motor vehicles.

The inventive hollow-chamber profile offers greater output thanpreviously known extruded profiles with parallel webs and unshapednarrow sides, because better convection is achieved without any loss ofthe heat transfer performance attributable to the turbulence produced bythe shaping of the webs and narrow sides transversely to the flow of gasor liquid.

A hollow-chamber profile of this type can be produced easily. In thefirst step of the process, a hollow profile strand, such as a round tubeprofile strand, a coaxial tube profile strand, or a flat tube profilestrand with two parallel wide sides and curved or flat narrow sides isproduced by extrusion so that at least one channel extends down theinterior space of the base profile. The hot, hollow profile strandemerging from the shaping zone of the extruder is caused to oscillate ina defined manner by an oscillating shaping tool and is thus shaped. Theshaped hollow profile strand can then be cut to the length desired forthe hollow-chamber profile and can be provided, if desired, withstampings at the ends of the tubes. These stampings make it easier topush the tubes into the manifolds and also make it easier to braze thetubes together effectively to form a heat exchanger.

The hot, hollow profile strand emerging from the shaping zone ispreferably subjected to the action of a shaping tool which oscillates inthe direction perpendicular to the exit direction of the profile strand.At the same time, both the narrow sides of the flat tube profile or theoutside surface of the round tube profile and any webs which may bepresent are shaped.

In a special embodiment, the shaping of the sides and of the websconsists of corrugations extending down the length of the base profile.The wavelength of a set of corrugations of this type preferably remainsthe same over the entire length of the hollow profile strand. This isachieved by adapting the oscillation frequency of the shaping tool tothe exit speed of the hollow profile strand. During the production ofmulti-chamber hollow profiles, extrusion speeds of 15-200 m/minute, andpreferably of 60-150 m/minute, are used. The wavelengths of thecorrugations of the profile strand can be on the order of 1-100 mm.

The shaping of the flat tube profile strand, that is, its deflection,occurs preferably in the direction of the tube width, so that the widesides retain their parallelism and are not deformed. This offers theadvantage that the following steps of the process of fabricating heatexchangers, especially the connection to the cooling fins and manifolds,can be done very easily.

It is also possible, however, to control two different planes ofoscillation separately from each other and thus to produce circularcorrugations. This can be advantageous especially when round tube orcoaxial tube profiles are being produced.

The oscillating movement of the shaping tool produces a deflection forcetransverse to the exit direction of the hollow profile strand. Thisdeflection can be brought about by mechanical forces in the form ofpressure and thrust. The hollow profile strand can also be deflected byelectromagnetic forces. An especially reliable way of deflecting thehollow profile strand is to use a fluid medium to actuate the shapingtool. Air, nitrogen, or even water can be used here.

An essential aspect of the inventive process is that the hollow profilestrand is shaped while it is hot. This can be achieved by locating theshaping tool in the immediate vicinity of the extrusion die. Thus thehollow profile strand cools down to only a negligible extent after itemerges from the extrusion die and before it is treated by the shapingtool. The temperature of the hollow profile strand in the shaping toolshould be greater than 250° C., and preferably greater than 400° C., inorder to arrive at the desired shape with little or no deformation. Whenthe hot, hollow profile strand emerging from the extruder is now grippedand deflected by the oscillating shaping tool, the deflection forces actall the way back to the extruder die and influence the flow of materialthere. A shaping tool of this type can be located, for example, in arecess in the cross-brace of the extruder.

It is also conceivable, however, that the hollow profile strand emergingfrom the extruder die could be carried away from the extruder. In thiscase, it is advantageous to provide an appropriate device for guidingthe profile strand between the extruder and the shaping device. Here,too, the high exit temperature of the hollow profile strand is used tomake shaping possible without deformation. Nevertheless, it must beguaranteed that the hollow profile strand has the desired shapingtemperature of more than 250° C. in the shaping tool.

In another embodiment of the inventive process, it is provided that theextruder die itself acts as an oscillating shaping tool. The extruderdie or the components of the system or tools which position the die inthe extruder perform an oscillating movement during the extrusionprocess.

The process according to the invention makes it possible to obtainhollow chamber profiles with corrugated shapes, where, in contrast tothe state of the art, the corrugations in question can be produced in adefined manner; that is, the corrugations have reproducible amplitudesand/or wavelengths. As a result, a hollow chamber profile is producedwhich has the same free flow cross section and the same wall thicknessesat all points along the entire length of the profile. The heat-exchangesurface is increased without causing significant pressure losses in theprofile. At the same time, the laminar flow is disrupted by thecorrugations. The turbulence thus created provides an advantageousincrease in the heat-exchange output of the profile.

Additional features, advantages, and advantageous embodiments of theinvention can be derived from the following description of theinvention, which is based on the attached drawings:

FIG. 1 shows a perspective view of an inventive hollow-chamber profile;

FIG. 2 shows a cross section through the hollow-chamber profile of FIG.1;

FIG. 3 shows a longitudinal section through the hollow-chamber profilealong line III-III of FIG. 1;

FIG. 4 a shows a diagrammatic representation of an inventive processvariant for a round tube profile;

FIG. 4 b shows a diagrammatic representation of the inventive processvariant according to FIG. 4 a for a flat tube profile; and

FIG. 5 shows a diagrammatic representation of another inventive processvariant.

FIG. 1 shows an inventive hollow-chamber profile made of metal. Itconsists preferably of an extruded base profile 10 of light metal. Thisbase profile 10 has at least one channel 11 oriented in the longitudinaldirection of the base profile 10, and preferably several channels 11.These channels 11 are bounded by the wall 12 and by the webs 13. Thebase profile 10 can also have web extensions (not shown), which arelocated on the inside surfaces of the wall 12, extending into thechannels 11 and parallel to the webs 13. As can be derived from FIGS. 1and 2, the base profile 10 has two parallel wide sides 16, 17, whichform the flat top and bottom of the profile. This is advantageous whenthe profile is to be used as a heat-exchanger profile. It facilitatesinstallation and the connection of the cooling fins to the top andbottom of the base profile 10.

An inventive hollow-chamber profile can also have the form of a roundtube or of a coaxial tube and have one or more channels oriented in thelongitudinal direction of the profile.

The corrugations provided to increase the heat-exchange output of theprofile pertain here exclusively to the narrow sides 18, 19 and to thewebs 13. The narrow sides 18, 19 are shaped perpendicularly to thelongitudinal orientation of the base profile, where left-orientedprofilings 21 and right-oriented profilings 22 alternate with oneanother along the two narrow sides 18, 19 and also along the webs 13. Asis especially clear in FIG. 3, the base profile 10 has a width B, which,in spite of the corrugations along each long side of the profile, is thesame at all points. The reason for this is that the two narrow sides 18,19 are profiled in the exactly same way; that is, they have exactly thesame the wave-like pattern. The webs 13 also have the same wave-likepattern. At any two arbitrary points along the base profile 10, thedistances A between the two adjacent webs 13 will always be the same.The distances C between the narrow side 18 and the first web 13′ and thedistances D between the narrow side 19 and the last web 13″ are alsoconstant. This means that any arbitrary cross section of the baseprofile 10 according to FIG. 1 has the same cross section as thataccording to FIG. 2; that is, the base profile 10 always has the samefree flow cross section at all points in the longitudinal direction. Inspite of the corrugations, it is therefore impossible for significantpressure losses to occur in the inventive base profile 10, because thereare no resistances which could negatively affect the flow.

The narrow sides 18, 19 and the webs 13 of the base profile 10 shown inFIGS. 1 and 3 are advantageously shaped with sets of corrugationsextending in the longitudinal direction, where the wavelengths of thevarious sets of corrugation remain uniform throughout. The profilings21, 22 of the narrow sides 18, 19 and of the webs 13 also all have thesame maximum deflection, that is, the same amplitude. A design of thistype is not mandatory with respect to achieving a high heat-exchangeoutput. As long as the free flow cross section remains constant, thewavelengths and/or amplitudes of the corrugations can also vary. Thepreviously described embodiment, however, is easier to manufacture.

How an inventive hollow-chamber profile made of metal can be providedwith defined, reproducible corrugations is described on the basis of twoalternative embodiments of the process according to FIGS. 4 a and 4 band FIG. 5.

A hollow profile strand 20 is produced by extrusion in the conventionalmanner. Only the extrusion die 33 of the extruder and its die chambers34, 35 are shown in FIGS. 4 a, 4 b, and 5. The extruder can be a directextruder known according to the state of the art, an indirect extruder,or an extruder for the conform process. The profile strand 20 with thedesired profile shape is extruded in the exit direction 36 from theextrusion die 33. In the embodiment according to FIGS. 4 a and 5, around tube is obtained, and in the embodiment according to 4 b, a flattube profile with several channels 11 is obtained. In the conventionalcase, the hot, hollow profile strand 20 is sent along a cooling bed tovarious stations so that additional processes such as coating, shaping,or cutting to length can be carried out. In the device shown in FIGS. 4a and 4 b, the hollow profile strand 20 has a straight profile strandsection BI extending up as far as a guide 37. This straight profilestrand section BI is followed by a shaped profile strand section BII.The shaping produces left-oriented profilings 21 and right-orientedprofilings 22, which are produced by a shaping tool 30. This shapingtool 30 moves in the shift direction 31 to produce a left-orientedprofiling 21 in the hollow profile strand 20 and then in the shiftdirection 32 to form a right-oriented profiling 22. The shaping tool 30is an oscillator, which oscillates at a frequency f adapted to theextrusion speed and thus to the strand exit speed v in order to achievethe desired wavelength 1 for the hollow-chamber profile 10. Theoscillation frequency f of the shaping tool 30 can be adjusted on thebasis of the following formula:F=v/1where:

-   -   f=the oscillation frequency in Hz (1/s);    -   v=the strand exit speed in m/s; and    -   l=the wavelength in m.

At a strand exit speed of 1 m/s (60 m/min) and a desired wavelength 1 of0.005 m (5 mm), an oscillation frequency of f=200 Hz would be set forthe shaping tool. The extrusion speeds v for hollow-chamber profiles,especially for MP profiles (multiport profiles) or MMP profiles(micro-multiport profiles) are in the range of 15-200 m/min, andpreferably 60-150 m/min. The wavelengths 1 of the inventive corrugationsare on the order of 1-100 mm.

The oscillating movement of the shaping tool 30, the force of whichproduces a deformation when it meets the hollow profile strand 20, canbe realized in various ways. For example, a system operated by anelectric motor or a cam drive can be used, or a hydraulic system can beused.

The hollow profile strand 30 could also be deflected by electromagneticforces.

To achieve the desired shaping without deformation, the shapingtemperature of the hollow profile strand 20 in the shaping tool 30should be at least 250° C.; preferably, however, it should be more than400° C. If, as a result of the layout of the production plant as awhole, the straight section BI of the profile strand is so long that thetemperature of the hollow profile strand 20 drops significantly below250° C., a heating device must be provided between the outlet of theextrusion die 33 and the shaping tool 30 to keep the hollow profilestrand 20 at the desired shaping temperature in the shaping tool 30. Ifthe length of the straight section BI of the profile strand is veryshort, there is no need to take measures to heat it.

FIG. 5 shows another diagram of a design of a device for an inventiveprocess. A separate guide 37 is omitted here. The shaping tool 30 alsoassumes the function of guiding the hollow profile strand 20. In thiscase, however, the deflection forces, which are produced by the shapingtool 30 as it moves in the shift directions 31, 32, act all the way backto the die 33 and influence the flow of material there. In this case,the hollow profile strand 20 does not have any straight section BI afteremerging from the die 33. Because the flow of the material of the hollowprofile strand 20 is affected all the back to the shaping zone, theprofilings 21, 22 are formed as soon as the strand emerges from the tooland are therefore already present in the area between the die 33 and theshaping tool 30. It is advantageous for the shaping tool 30 to have awidth BIII in the exit direction 36 which is at least twice thewavelength 1 of the corrugated profilings.

A shaping tool 30 of this type, which represents an oscillating guidefor the strand, is preferably mounted on the extruder itself. Inparticular, a shaping tool 30 of this type can be located and guided ina recess in the cross-brace of the extruder.

LIST OF REFERENCE NUMBERS

-   10 base profile-   11 channel-   12 wall-   13, 13′, 13″ web-   14 open end of 10-   15 open end of 10-   16 wide side-   17 wide side-   18 narrow side-   19 narrow side-   20 hollow profile strand-   21 left-oriented profiling-   22 right-oriented profiling-   23 interior space-   30 shaping tool/oscillator-   31 shift direction-   32 shift direction-   33 extrusion die-   34 die chamber-   35 die chamber-   36 exit direction of 20-   37 guide-   A distance between adjacent webs-   B width of 10-   BI straight section of the profile strand-   BII shaped section of the profile strand-   BIII width of 30-   C distance between wide side 18 and web 13′-   D distance between wide side 19 and web 13″

1. Hollow-chamber profile made of metal, especially for heat exchangers,consisting of an extruded base profile (10) with two parallel wide sides(16, 17) and two narrow sides (18, 19), where at least one channel (11)extends in the longitudinal direction of the base profile (10) throughthe interior space (23) in the base profile (10), wherein the narrowsides (18, 19) are shaped in the direction perpendicular to thelongitudinal dimension of the base profile (10), where left-orientedprofilings (21) transverse to the longitudinal dimension andright-oriented profilings (22) transverse to the longitudinal dimensionalternate with each other along the two narrow sides (18, 19), and wherethe width (B) of the base profile (10) is the same over the entirelength of the base profile (10), the narrow sides with the profilingshave a uniform wall thickness along the entire length of the profile. 2.Hollow-chamber profile according to claim 1, wherein webs (13), whichextend from wide side (16) to wide side (17) and form several channels(11), are located in the interior space (23) of the base profile (10),and in that these webs (13) have profilings (21, 22) perpendicular tothe longitudinal dimension of the base profile (10), where the distance(A) between two adjacent webs (13), the distance (C) between the narrowside (18) and the first web (13′), and the distance (D) between thenarrow side (19) and the last web (13′) are the same over the entirelength of the base profile (10).
 3. Hollow-chamber profile according toclaim 2, wherein the profilings (21, 22) of the narrow sides (18, 19)and of the webs (13) form a wave-like pattern extending down the lengthof the base profile (10), such that the base profile (10) has the samefree flow cross section at all points along its length. 4.Hollow-chamber profile according to claim 3, wherein the wavelikepatterns formed by the narrow sides (18, 19) and the webs (13) have thesame wavelength over the entire length of the base profile (10). 5.Hollow-chamber profile according to claim 1, wherein the base profile(10) is manufactured of aluminum or an aluminum alloy.
 6. Hollow-chamberprofile according to claim 1, wherein it is used as a cooler for gas orliquid streams, especially as a gas cooler or as a charge cooler formotor vehicles.